# NOTE: The next line is critical for boot!
proc /proc proc defaults 0 0

# glibc 2.2 and above expects tmpfs to be mounted at /dev/shm for
# POSIX shared memory (shm_open, shm_unlink).
# (tmpfs is a dynamically expandable/shrinkable ramdisk, and will
# use almost no memory if not populated with files)
shm /dev/shm tmpfs nodev,nosuid,noexec 0 0

Also, right now fstab assumes your /boot is ext2 and / is ext3. If those aren't correct, change them to the filesystem you set them up to at the begining of the instalation. And I'm pretty sure that if you used ReiserFS, that you need to compile those modules into the kernel, then re-compile your kernel.

If that dosen't work, sorry. But i'm also no expert in Gentoo, but I'm learning.